Process for preparing epoxy resins having improved physical properties when cured

ABSTRACT

Epoxy resins having improved properties are prepared by reacting an epoxy resin with a dihydric phenol in the presence of a sufficient quantity of a phosphonium catalyst such that the product resulting from reacting a mixture of the catalyst, epoxy resin and dihydric phenol has a % epoxide difference from the theoretical percent epoxide of from about 0.5 to about 4.0.

This is a divisional of application Ser. No. 212,959, filed Dec. 4,1980, now U.S. Pat. No. 4,352,918.

BACKGROUND OF THE INVENTION

Epoxy resins have heretofore been advanced in the presence ofphosphonium catalysts disclosed by Dante in U.S. Pat. No. 3,477,990 andPerry in Canadian Pat. No. 893,191 and U.S. Pat. No. 3,948,855. However,the quantities of catalyst employed were that which would provide aresin having a percent epoxide value sufficiently close to thetheoretical epoxide value that no improvement in properties wereenvisioned.

The process of the present invention provides for the production ofadvanced epoxy resins having an improvement in one or more physicalproperties such as, for example, reactivity, glass transitiontemperature of the cured resins and the like. Resins having fasterreactivity characteristics provide for increased productivity ofarticles produced therefrom over a unit time period. The increase inglass transition temperature of a cured resin permits articles preparedtherefrom to be employed in higher temperature environments. Cured epoxyresins having increased glass transition temperatures provide productswhich can be employed in environments of higher temperatures i.e., theuseful operating temperature is generally directly proportional to theglass transition temperature.

SUMMARY OF THE INVENTION

The present invention pertains to an improvement in a process foradvancing epoxy resins in molecular weight by reacting (A) an epoxyresin which is a glycidyl ether of a dihydric phenol having an averageof more than one glycidyl ether group per molecule with (B) a dihydricphenolic compound in the presence of (C) a phosphonium catalystemploying components (A) and (B) in quantities such that the phenolichydroxyl to epoxide equivalent ratio is that which will provide atheoretical percent epoxide of the resultant reaction product of fromabout 2.7 to about 14, preferably from about 7 to about 12.5; whereinthe improvement comprises employing the catalyst, component (C) in aquantity such that the epoxy resin which would result when subjecting amixture of components (A), (B) and (C) to suitable reaction conditionsproduces an advanced epoxy resin wherein the difference obtained bysubtracting the percent epoxide obtained by analysis from thetheoretical percent epoxide is from about 0.5 to about 4, preferablyfrom about 1 to about 2; thereby providing an epoxy resin which whencured with a curing quantity of a curing agent provides a compositionwhich has an improvement in one or more of the properties selected fromthe group consisting of glass transition temperature and increasedreactivity.

The present invention also pertains to products resulting from curing amixture of an epoxy resin prepared by the above procedure and a curingquantity of a curing agent therefor.

The present invention also pertains to an improvement in a process forpreparing resin impregnated substrates for use in preparing electricallaminates by a process which comprises:

(I) saturating said substrate with a resin forming mixture comprising;

(A) an epoxy resin having an epoxide equivalent weight of from about 300to about 600, preferably from about 375 to about 475 which has beenprepared by reacting

(1) a glycidyl ether of a dihydric phenol having an average of more thanone epoxide group per molecule and an epoxide equivalent weight (EEW) offrom about 156 to about 400, preferably from about 177 to about 190,with

(2) a dihydric phenolic compound in the presence of

(3) a phosphonium catalyst for effecting the reaction between (1) and(2), wherein components (1) and (2) are employed in quantities whichwill provide a theoretical percent epoxide of the reaction product offrom about 8 to about 15, preferably from about 9.5 to about 13;

(B) a curing agent for said epoxy resin and

(C) a solvent system for Components A and B;

(II) heating the resultant impregnated substrate to B-stage the resinand remove the solvent system; the improvement which comprises:

employing as the catalyst, Component (A-3), a phosphonium salt orcomplex thereof which has at least one, preferably two, most preferablythree aromatic ring(s) attached to the phosphorus atom of thephosphonium group and at least one aliphatic hydrocarbon group attachedto said phosphorus atom, said catalyst being employed in a quantity suchthat the epoxy resin which would result when subjecting a mixture ofcomponents (A-1), (A-2) and (A-3) to suitable reaction conditionsproduces an advanced epoxy resin wherein the difference obtained bysubtracting the precent epoxide obtained by analysis from thetheoretical percent epoxide is from about 0.5 to about 4, preferablyfrom about 1 to about 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Suitable glycidyl ethers of a dihydric phenol which can be employed inthe present invention include those represented by the formula ##STR1##wherein A is a divalent hydrocarbon group having from 1 to about 8carbon atoms, --S--, --S--S--, --O--, ##STR2## each X is independentlyhydrogen, chlorine or bromine; x has a value of zero or one and n has avalue such that the EEW is from about 156 to about 400, preferably fromabout 177 to about 190, calculated on the basis of X being hydrogen.

Particularly suitable are the diglycidyl ethers of bisphenol A andtetrabromobisphenol A.

Suitable dihydric phenolic compounds include, for example, catechol,hydroquinone, resorcinol and bisphenols such as those represented by theformula ##STR3## wherein X, A and x are as defined above.

Particularly suitable dihydric phenolic compounds are bisphenol A andtetrabromo bisphenol A.

Suitable phosphonium catalysts which can be employed herein include, forexample, those compounds having at least one phosphonium cation grouprepresented by the formula ##STR4## wherein each R is independently ahydrocarbyl or substituted hydrocarbyl group having from 1 to about 20,preferably from 1 to about 6, carbon atoms or substituted hydrocarbylgroups. It is preferred that at least one, preferably two and mostpreferably three, of the R groups be an aromatic group i.e., an arylgroup or an alkaryl group such that the phosphorus atom is attacheddirectly to the aromatic ring of such aryl or alkaryl group.

By the term hydrocarbyl, it is meant that the groups can be alkyl, aryl,alkaryl, aralkyl and the alkyl can be either cyclic or acyclic. Bysubstituted hydrocarbyl it is meant that the hydrocarbyl groups cancontain one or more inert substituent groups such as, for example, Cl,Br, I, NO₂, mixtures thereof and the like.

The R groups can contain any substituent group which is inert to thesystem, i.e. will not deactivate the catalyst under the conditions inwhich they are employed.

It is preferred that the phosphonium cation contain at least onearomatic ring and at least one alkyl group attached directly to aphosphorus atom.

Suitable anions include the halides, such as, for example, Cl, Br, I,carboxylates, dicarboxylates, phosphates, nitrates, sulfates, nitrites,sulfites, borates, chromates, mixtures thereof and the like.

The preferred anions are the strong acids, i.e. those having a pK_(a)value less than about 4.5, preferably less than about 3.7, because thecatalysts containing such are generally more efficient, in that it takesless catalyst to effect the lowering of the epoxide value to the desiredvalue below the theoretical value.

The dihydric phenol and the glycidyl ether of a dihydric phenol areemployed in quantities such that the theoretical percent epoxide of theresultant product is from about 2.7 to about 14, preferably from about 7to about 12.5.

The quantity of catalyst will of course vary depending upon theparticular catalyst employed; however, for most catalysts, from about0.1 to about 1.5, preferably from about 0.2 to about 0.8, parts catalystby weight per 100 parts by weight of glycidyl ether of dihydric phenolcan be employed.

The reaction conditions employed to prepare the advanced epoxy resinscan vary, but temperatures of from about 100° C. to about 200° C.,preferably from about 120° C. to about 160° C., are suitable. Lowertemperatures usually require longer reaction times whereas highertemperatures usually require shorter reaction times.

The pressure employed is not particularly important and can be fromabout 1 mm Hg vacuum to about 100 psig. However, it is usually preferredto employ pressures of from about 5 psig to about 20 psig.

The particular reaction conditions are not important so long as for theparticular phosphonium catalyst and quantity thereof employed, thereaction conditions produce the desired result i.e., the resultantadvanced epoxy resin has the required difference between the theoreticalpercent epoxide and the actual percent epoxide value obtained byanalysis.

Any of the well known curing agents can be employed in the presentinvention to cure the epoxy resins. Such curing agents include amines,amides, guanidines, phenolic hydroxyl-containing materials, carboxylicacids, carboylic acid anhydrides, imidazoles, biguanides, mixturesthereof and the like.

Particularly suitable curing agents include, for example, guanidinessuch as for example, dicyandiamide and tetramethyl guanidine andbiguanides such as 1,6-xylene biguanide, polyhydric phenols, mixturesthereof and the like

The quantity of curing agent employed depends upon the particular curingagent employed and the properties desired in the resultant cured resin,all of which is well known by those persons reasonably skilled in theart and discussed in HANDBOOK OF EPOXY RESINS, by Lee and Neville,McGraw Hill, 1967, which is incorporated herein by reference.

The theoretical percent epoxide is calculated by the following formula##EQU1## EqER=epoxide equivalents from the epoxy resin. EqDHP=phenolichydroxyl equivalents from the dihydric phenol.

WtER÷weight of epoxy resin employed.

WtDHP=weight of dihydric phenol employed.

The actual percent epoxide was determined experimentally by titrationwith perchloric acid in glacial acetic acid by the liberation ofhydrogen bromide generated by the addition of tetraethylammonium bromidein glacial acetic acid using crystal violet as an indicator. The epoxygroups react stoichiometrically with hydrogen bromide generated from thereaction of perchloric acid with tetraethyl ammonium bromide. When theepoxy groups have been reacted, the free hydrogen bromide causes thecrystal violet to change color.

The glass transition temperature, Tg, was determined by the method ofASTM D3418-75 on cured specimens prepared in the following manner. Amixture of 10 grams of the resultant epoxy resin, 0.3 gram ofdicyanandiamide and 0.01 gram of 2-methyl imidazole was melt mixed on a100° C. hot plate for 3 minutes. The mixture was finely ground in amortar and pestle. The powder was transferred to an aluminum weighingdish and cured at 175° C. for 2 hours.

The stroke cure reactivity was determined by the following procedure.

An acetone solution of epoxy resin is prepared by blending 10 grams ofacetone with 30 grams of molten epoxy resin warmed to 80°-100° C. Thesolution is allowed to cool to room temperature and then 9 grams of a10% solution of dicyandiamide in the monomethylether of ethylene glycoland 0.75 gram of a 10% solution of benzyldimethylamine (BDMA) in acetoneis added (3 phr dicy, 0.25 phr BDMA). The solution is mixed well andallowed to stand at room temperature for a period of 2 hours. Thecatalyzed resin is then drawn in an eye dropper and placed on a hotplateat 175° C.±1° C. The stop watch is immediately started. Allow sample torest on the hotplate undisturbed for 60±1 seconds. At this point, beginstroking with a wooden spatula. Stroking should be done by pushing theresin puddle back and forth over an area about 1 square inch using thesame side of the spatula in contact with the resin. The resin willthicken as it is continuously stroked. Eventually the resin will becomestringy and immediately after, becomes a rubber gel that releases fromthe hotplate. This is the end point. Stop the stopwatch and record thereading. The fewer the number of seconds, the higher the reactivity.

The following examples are illustrative of the present invention, butare not to be construed as to limiting the scope thereof in any manner.

Various catalysts employed in the examples and comparative experimentswere prepared by the following procedures.

CATALYST PROCEDURE A

To a single necked 100 ml round bottom flask (RBF) was charged theparticular phosphonium catalyst precursor as a 70% solution in methanol.The particular acid employed was dissolved in methanol and charged tothe RBF. The solvents and excess acetic acid were removed under vacuumwhile heating to a final temperature of 75° C. at 1 mm Hg. The resultantliquor was acetone washed thereby yielding a white solid phosphoniumsalt of the acid employed.

CATALYST PROCEDURE B

To a 500 ml single neck RBF was charged the particular precursor as a70% solution in methanol. The particular acid employed was slowly addedto the solution while stirring the flask. The solvent and excess aceticacid were removed under vacuum while heating to a final temperature of120° C. at 1 mm Hg. The resultant product was acetone washed therebyyielding the phosphonium salt of the acid employed.

CATALYST PROCEDURE C

To a single neck 500 ml RBF was charged the phosphonium bicarbonateprecursor in methanol. The particular acid employed was dissolved inmethanol in a beaker and then slowly added to the RBF while swirling theRBF. Swirling was maintained until CO₂ evolution subsided. The solutionwas then rotoevaporated until a vacuum could be maintained at 1 mm Hg at75° C. The resultant liquor was washed twice with acetone to removeexcess acid impurities to yield a white solid phosphonium salt of theacid.

CATALYST PROCEDURE D

To a one inch diameter glass column equipped with a stopcock was chargeda methanol slurry of 65 g (70% by weight H₂ O) of an anion exchangeresin in the acetate form (200-400 mesh; 0.8 meq. per ml resin bed; 3.5meq. per dry gram; 70-78 wt.% moisture; styrene type quaternaryammonium; wet mesh range 80-200) available from BIO·RAD Laboratories asAG1-X2. A 5% solution in methanol of potassium hydroxide was slowlyeluded through the column at a rate of 2 drops per second. The columnwas then washed with methanol until neutral to litmus paper. Thephosphonium catalyst precursor, as a 70% solution in methanol, was thenadded to the column and slowly eluded through the ion exchange resinuntil the dark band was washed through the column. The eluded materialwas caught in a RBF containing an excess molar ratio of the acid. Thissolution was then rotoevaporated and acetone washed to yield a whitesolid phosphonium salt of the acid.

CATALYST PROCEDURE E

To a 4 oz bottle was charged 100 g (0.17 mol) of a 70% methanol solutionof ethyltriphenylphosphonium acetate·acetic acid complex followed by theaddition of 20.44 g (0.1622 mol) of oxalic acid dihydrate. The mixturewas mixed until all of the oxalic acid had dissolved. The resultantsolution contained about 51.14 wt.% ethyltriphenylphosphonium oxalate.

CATALYST PROCEDURE F

To a 2 gallon bottle was charged 1000 g (1.707 mol) of a 70% methanolsolution of ethyltriphenylphosphonium acetate·acetic acid complexfollowed by the addition of 204.4 g (1.622 mol) of oxalic aciddihydrate. The mixture was mixed until all the oxalic acid had dissolvedand then about 31.5 g of methanol was added to give a resultant solutionof about 50 wt. % ethyltriphenylphosphonium oxalate.

The precursors and acids employed, reaction conditions and results areprovided in the following Table I for which the abbreviations employedtherein have the following meaning.

BTPP=butyltriphenylphosphonium

ClAc=chloroacetate

ETPP=ethyltriphenylphosphonium

ETPPAc·HAc=ethyltriphenylphosphonium acetate·acetic acid complex

HCO₃ =bicarbonate

                                      TABLE I                                     __________________________________________________________________________                          ACID EMPLOYED    PRECURSOR EMPLOYED                     No.                                                                              CATALYST   PROCEDURE                                                                             TYPE   g/moles                                                                              pKa                                                                              TYPE    g/moles                                                                             pKa                      __________________________________________________________________________    1  BTPP FORMATE                                                                             C       Formic 2.73/0.06                                                                            3.6                                                                              BTPPHCO.sub.3                                                                         13.2/0.035                                                                          6.5                      2  ETPP FORMATE                                                                             C       Formic 2.73/0.06                                                                            3.6                                                                              ETPPHCO.sub.3                                                                         13.2/0.035                                                                          6.5                      3  ETPP FORMATE                                                                             D       Formic 4.1/0.09                                                                             3.6                                                                              ETPPAc.HAc                                                                            3.5/0.009                                                                           4.6                      4  BTPP OXALATE                                                                             C       Oxalic 2.47/0.027                                                                           1.3                                                                              BTPPHCO.sub.3                                                                         9.9/0.026                                                                           6.5                      5  ETPP PHOSPHATE                                                                           B       Phosphoric                                                                           6.38/0.065                                                                           2.1                                                                              ETPPAc.HAc                                                                            26.7/0.0651                                                                         4.6                      6  ETPP SUCCINATE                                                                           B       Succinic                                                                             14/0.119                                                                             4.2                                                                              ETPPAc.HAc                                                                            48.8/0.119                                                                          4.6                      7  ETPP MALONATE                                                                            B       Malonic                                                                              1.56/0.016                                                                            2.85                                                                            ETPPAc.HAc                                                                            5.88/0.014                                                                          4.6                      8  ETPP OXALATE                                                                             A       Oxalic 1.94/0.015                                                                           1.2                                                                              ETPPAc.HAc                                                                            6.3/0.015                                                                           4.6                      9  BTPPClAc   C       Chloro-acetic                                                                        2.84/0.03                                                                            2.9                                                                              BTPPHCO.sub.3                                                                         9.9/0.026                                                                           6.5                      10 ETPP OXALATE                                                                             E       Oxalic 20.44/0.1622                                                                         1.2                                                                              ETPPAc.HAc                                                                            70/0.171                                                                            4.6                      11 ETPPAc.HAc Purchased from Cincinatti Milacron, Inc.                        12 ETPP OXALATE                                                                             F       Oxalic 204.4/1.622                                                                          1.2                                                                              ETPPAc.sup.˜ HAc                                                                700/1.71                                                                            4.6                      __________________________________________________________________________                   METHANOL                                                                      SOLVENT REACTION                                                                             MELTING POINT                                                  (total Quant.)                                                                        TEMP.  AND YIELD                                                   No.                                                                              grams   °C.                                                                           °C./%                                                                            COMMENTS                              __________________________________________________________________________                 1 37      100    190/N.D..sup.1                                                                          white solid                                       2  37      100    N.A..sup.2 /N.D.                                                                        brown liquid                                      3  200     100    N.A./95   brown liquid                                      4  35      75     155/78    white solid                                       5  11      25     175-189/100                                                                             white solid                                       6  21      120    N.A./N.D. brown liquid                                      7  40      120    N.A./N.D. brown liquid                                      8  23      70     151/91    white solid                                       9  13      75     212-215/76                                                                              white solid                                       10 30      25     N.A./N.D. mixture contains free acetic                                                  acid                                              11 N.A.    N.A.   N.A.      70% solution in methanol                          12   81.6  25     N.A./N.D. mixture contains free acetic          __________________________________________________________________________                                            acid                                   .sup.1 N.D. -- not determined                                                 .sup.2 N.A. = not applicable                                             

GENERAL PROCEDURE FOR RESIN PREPARATION

To a reaction vessel equipped with a means for stirring, temperaturecontrol and indication and nitrogen purge was charged the desired weightof the specified liquid diglycidyl ether of bisphenol A and the desiredweight of the specified dihydric phenol. The mixture was heated at arate of 5° C./minute. When the temperature of the mixture reached 70°C., the desired amount of the specified phosphonium catalyst dissolvedin methanol was added. The mixture was heated at the desired reactionconditions to give the resultant product.

EPOXY RESIN A

Epoxy Resin A was a liquid diglycidyl ether of bisphenol A having anaverage epoxide equivalent weight of about 189, % epoxide of about22.75% and an aliphatic chloride content of about 3410 ppm.

EPOXY RESIN B

Epoxy Resin B was a liquid diglycidyl ether of bisphenol A having anaverage epoxide equivalent weight of about 188, % epoxide of about22.82% and an aliphatic chloride content of about 3700 ppm.

EPOXY RESIN C

Epoxy Resin C was a liquid diglycidyl ether of bisphenol-A having anaverage epoxide equivalent weight of about 186.5, % epoxide of about23.06 and an aliphatic chloride content of about 2200 parts per million.

DIHYDRIC PHENOL A

Dihydric phenol A was tetrabromobisphenol A having a phenolic hydroxylequivalent weight of about 272 and percent bromine content of about58.8%.

DIHYDRIC PHENOL B

Dihydric phenol B was a bisphenol A having a phenol hydroxyl equivalentweight of about 114.

EXAMPLES 1-21 AND COMPARATIVE EXPERIMENTS A-G

The components, reaction conditions and results are given in thefollowing Table II.

                                      TABLE II                                    __________________________________________________________________________    EX.                      REACTION           AC-                               OR   EPOXY               CONDITIONS         TUAL DIFF.                                                                             175° C.           COMP.                                                                              RESIN                                                                              DIHYDRIC       1st                                                                              2nd                                                                              3rd 4th                                                                              THEORY                                                                              %    IN %                                                                              STROKE                   EXPT.                                                                              Type/                                                                              PHENOL CATALYST                                                                              Hour                                                                             Hour                                                                             Hour                                                                              Hour                                                                             %     EPOX-                                                                              EPOX-                                                                             CURE  Tg                 NO.  Equiv.                                                                             Type/Equiv.                                                                          Type/moles                                                                            °C.                                                                       °C.                                                                       °C.                                                                        °C.                                                                       EPOXIDE                                                                             IDE  IDE Sec.  °C.         __________________________________________________________________________    A    A/1.244                                                                            A/0.422                                                                              No. 10/0.0002                                                                         120                                                                              130                                                                              150 150                                                                              10.1  10   0.1 289   103                B    A/1.164                                                                            A/0.333                                                                              No. 10/0.00022                                                                        120                                                                              130                                                                              150 150                                                                              11.5  11.48                                                                              0.02                                                                              320   109                 1   A/11.64                                                                            A/3.33 No. 10/0.0087                                                                         120                                                                              130                                                                              150 150                                                                              11.5  10.97                                                                              0.53                                                                              310   117                 2   A/11.64                                                                            A/3.33 No. 10/0.0174                                                                         120                                                                              130                                                                              150 150                                                                              11.5  10.9 0.6 305   N.D..sup.2          3   A/11.64                                                                            A/3.33 No. 10/0.013                                                                          120                                                                              130                                                                              150 150                                                                              11.5  10.76                                                                              0.74                                                                              305   121                 4   A/11.64                                                                            A/3.33 No. 10/0.0174                                                                         120                                                                              130                                                                              150 150                                                                              11.5  10.1 1.4 280   128                 5   A/11.64                                                                            A/3.33 No. 10/0.0256                                                                         120                                                                              130                                                                              150 150                                                                              11.5  10.05                                                                              1.45                                                                              268   131                 6   A/11.64                                                                            A/3.33 No. 10/0.0337                                                                         120                                                                              130                                                                              150 150                                                                              11.5  9.09 2.41                                                                              255   127                C    A/1.06                                                                             A/0.303                                                                              No. 11/0.00024                                                                        120                                                                              130                                                                              150 150                                                                              11.5  11.5 0   340   110                D    A/1.06                                                                             A/0.232                                                                              No. 11/0.00024                                                                        120                                                                              130                                                                              150 150                                                                              12.00 12   0   325   114                 7   A/1.335                                                                            A/0.359                                                                              No. 11/0.00730                                                                        120                                                                              130                                                                              150 150                                                                              12.00 10.21                                                                              1.79                                                                              269   127                 8   A/1.06                                                                             A/0.28 No. 8/0.0026                                                                          120                                                                              130                                                                              150 150                                                                              12.00 10.3 1.7 N.D.  N.D.                9.sup.1                                                                           A/1.06                                                                             A/0.28 No. 11/0.0026                                                                         120                                                                              130                                                                              150 150                                                                              12.00 10.2 1.8 N.D.  N.D.                                X.sup.1 /0.0026                                              10   A/23.12                                                                            A/6.21 No. 6/0.12                                                                            120                                                                              130                                                                              150 150                                                                              12.00 9.8  2.2 N.D.  N.D.               11   A/11.45                                                                            A.3.07 No. 5/0.0653                                                                          120                                                                              130                                                                              150 150                                                                              12.00 10.65                                                                              1.35                                                                              N.D.  130                12   A/1.114                                                                            A/0.3  No. 9/0.00277                                                                         120                                                                              130                                                                              150 150                                                                              12.00 10.66                                                                              1.34                                                                              290   127                13   A/1.09                                                                             A/0.293                                                                              No. 7/0.0038                                                                          120                                                                              130                                                                              150 150                                                                              12.00 11.00                                                                              1   293   N.D.               14   B/1.06                                                                             A/0.288                                                                              No. 1/0.0041                                                                          150                                                                              150                                                                              150 150                                                                              11.89 8.6  3.29                                                                              N.D.  N.D.               15   B/1.06                                                                             A/0.285                                                                              No. 3/0.003                                                                           120                                                                              130                                                                              150 150                                                                              12.00 10.00                                                                              2   N.D.  N.D.               16   B/1.06                                                                             A/0.285                                                                              No. 4/0.0026                                                                          120                                                                              130                                                                              150 150                                                                              12.00 9.8  2.2 N.D.  N.D.               17   B/1.06                                                                             A/0.288                                                                              No. 2/0.0032                                                                          150                                                                              150                                                                              150 150                                                                              11.89 10.2 1.69                                                                              N.D.  N.D.               18   A/22.14                                                                            B/7.94 No. 10/0.0664                                                                         120                                                                              130                                                                              150 150                                                                              12.00 9.8  2.2 205   130                E    A/1.04                                                                             B/0.29 No. 10/0.000097                                                                       150                                                                              150                                                                              N.A..sup.3                                                                        N.A.                                                                             14.00 13.99                                                                              0.01                                                                              274   N.D.               19   A/1.01                                                                             B/0.28 No. 10/0.00184                                                                        140                                                                              140                                                                              140 140                                                                              14.00 12.13                                                                              1.87                                                                              255   N.D.               F    A/1.02                                                                             B/0.72 No. 10/0.000184                                                                       150                                                                              150                                                                              150 N.A.                                                                             4.65  4.39 0.26                                                                              300   N.D.               20   A/1.58                                                                             B/1.12 No. 10/0.00288                                                                        155                                                                              155                                                                              155 155                                                                              4.65  3.51 1.14                                                                              280   N.D.               G    A/1.01                                                                             B/0.83 No. 10/0.00028                                                                        150                                                                              150                                                                              150 150                                                                              2.70  2.46 0.24                                                                              255   N.D.               21   A/1.01                                                                             B/0.83 No. 10/0.00185                                                                        195                                                                              195                                                                              195 195                                                                              2.70  1.70 1   164   N.D.               22   C/88.36                                                                            A/25.64                                                                              No. 12/0.15                                                                           120                                                                              130                                                                              160 N.A.                                                                             11.50 10.00                                                                              1.50                                                                              N.D.  130                __________________________________________________________________________     .sup.1 Insitu preparation of catalyst (ETPP Oxalate) by adding the            catalyst precursor (ETPPAc.HAc) plus acid (oxalic acid dihydrate              designated X) to the mixture of epoxy resin and dihydric phenol.              .sup.2 N.D. = not determined.                                                 .sup.3 N.A. = not applicable                                             

EXAMPLE 23 (PREPARATION OF ELECTRICAL LAMINATE) A. Preparation ofPrepreg Varnish Formulation

A prepreg varnish formulation was prepared by blending about 5411 g of a75% solution by weight in acetone of the resin of example #22 with about1225 g of a 10% solution of dicyandiamide in the monomethylether ofethylene glycol (˜3 phr dicyandiamide), about 6.13 g ofbenzyldimethylamine (˜0.15 phr BDMA) and about 200 g acetone. Theviscosity of the solution at 25° C. was 25 seconds using a #2 Zahn cup.The 175° C. stroke cure reactivity of the prepreg varnish was about 245seconds.

B. Preparation of Laminate

Fiberglass cloth (type 7628 with I399 finish) was impregnated by passingit through the prepreg varnish described in A above, followed by a pairof doctor bars set at 15 mils clearance to control resin pickup, andfinally through an oven at 300° F. for a dwell time of approximately 4minutes. The resulting B-staged impregnated cloth of prepreg had a geltime of 93 seconds at 175° C.

A laminate was then prepared from the above prepared preimpregnatedfiberglass employing 6 plys of 12 in.×12 in.×0.13 in. (3 cm×3 cm×0.33mm) sheets of 7628 style glass all of which were I399 finish. Thelaminate was prepared by pressing at 500 psig (3500 kg/cm²) for 60minutes at 175° C. The laminate was then tested.

The pressure cooker-solder test was conducted by

(i) cutting 2 in.×4 in. coupons from prepared laminate,

(ii) placing 3 coupons edgewise on a rack in a pressure cooker andmaintaining 15 psig steam pressure for ˜1.5 hour, and

(iii) then immersing the coupons in 500° F. solder for 20 seconds.

Six sides of the 3 coupons were evaluated and rated by the number ofsides passing. In order to pass, the side must be free of blisters afterimmersion in hot solder. A 1/2 side pass consisted of the side havingonly 1 edge blister.

The laminate had a glass transition temperature (Tg) of 130° C. Aftersubjecting to 15 psig steam pressure for 11/2 hours and immersion in500° F. solder for 20 seconds, 51/2 sides of the laminate out of sixsides passed the test.

We claim:
 1. In a process for preparing resin impregnated substrates foruse in preparing electrical laminates by a process which comprises:(I)saturating said substrate with a resin forming mixture comprising;(A) anepoxy resin having an epoxide equivalent weight of from about 300 toabout 600 which has been prepared by reacting(1) a glycidyl ether of adihydric phenol having an average of more than one epoxide group permolecule and an epoxide equivalent weight (EEW) of from about 156 toabout 400; with (2) a dihydric phenolic compound; in the presence of (3)a phosphonium catalyst for effecting the reaction between (1) and (2),wherein components (1) and (2) are employed in quantities which providea theoretical percent epoxide of the reaction product of from about 8 toabout 15; (B) a curing agent for said epoxy resin and (C) a solventsystem for Components (A) and (B); (II) heating the resultantimpregnated substrate to B-stage the resin and remove the solventsystem; the improvement which comprises: employing as the catalyst,Compound (A-3), a phosphonium salt or complex thereof which has at leastone aromatic ring attached to the phosphorus atom of the phosphoniumgroup and at least one aliphatic hydrocarbon group attached to saidphosphorus atom, said catalyst being employed in a quantity such thatthe epoxy resin which would result when subjecting a mixture ofcomponents (A-1), (A-2) and (A-3) to suitable reaction conditionsproduces an advanced epoxy resin wherein the difference obtained bysubtracting the precent epoxide obtained by analysis from thetheoretical percent epoxide is from about 0.5 to about
 4. 2. The processof claim 1 wherein (a) components (A-1) and (A-2) are employed inquantities which provide a theoretical percent epoxide of the reactionproduct of from about 9.5 to about 13; (b) component (A-3) has twoaromatic rings attached to the phosphorous atom; and (c) the differenceobtained by subtracting the percent epoxide obtained by analysis fromthe theoretical percent epoxide is from about 1 to about
 2. 3. Theprocess of claim 2 wherein component (A-1) is a glycidyl ether ofbisphenol A having an average epoxide equivalent weight of from about156 to about 400; (b) component (A-2) is bisphenol A; and (c) component(A-3) has three aromatic rings attached to the phosphorus atom.
 4. Theprocess of claim 3 wherein component (A-1) has an average epoxideequivalent weight of from about 177 to about
 190. 5. The process ofclaims 1, 2, 3 or 4 wherein the cation portion of said phosphoniumcatalyst is represented by the formula ##STR5## wherein each R isindependently a hydrocarbyl or substituted hydrocarbyl group having fromabout 1 to about 20 carbon atoms at least one of which contains at leastone aromatic ring attached directly to the phosphorus atom.
 6. Theprocess of claim 5 wherein said hydrocarbyl groups have from 1 to about6 carbon atoms and at least two of such R groups contain an aromaticring attached directly to the phosphorus atom and wherein the anionportion of the phosphonium catalyst is a halide, carboxylate,dicarboxylate, phosphate, nitrate, sulfate, nitrite, sulfite, borate orchromate.
 7. The process of claim 6 wherein the anion is adicarboxylate.
 8. The process of claim 7 wherein the catalyst is ethyltriphenyl phosphonium oxalate.
 9. The process of claim 6 wherein theanion is a carboxylate.
 10. The process of claim 9 wherein the catalystis ethyltriphenylphosphonium formate.
 11. A resin impregnated substrateprepared by the process of claims 1, 2, 3 or
 4. 12. A resin impregnatedsubstrated of claim 11 wherein the cation portion of said phosphoniumcatalyst is represented by the formula ##STR6## wherein each R isindependently a hydrocarbyl or substituted hydrocarbyl group having fromabout 1 to about 20 carbon atoms at least one of which contains at leastone aromatic ring attached directly to the phosphorus atom.
 13. A resinimpregnated substrate of claim 12 wherein said hydrocarbyl groups havefrom 1 to about 6 carbon atoms and at least two of such R groups containan aromatic ring attached directly to the phosphorus atom and whereinthe anion portion of the phosphonium catalyst is a halide, carboxylate,dicarboxylate, phosphate, nitrate, sulfate, nitrite, sulfite, borate orchromate.
 14. A resin impregnated substrate of claim 13 wherein theanion is a dicarboxylate.
 15. A resin impregnated substrate of claim 14wherein the catalyst is ethyl triphenyl phosphonium oxalate.
 16. A resinimpregnated substrate of claim 13 wherein the anion is a carboxylate.17. A resin impregnated substrate of claim 16 wherein the catalyst isethyltriphenylphosphonium formate.
 18. An electrical laminate preparedfrom one or more plies of a resin impregnated laminate, at least one ofsuch plies being a resin impregnated laminate of claim
 11. 19. Anelectrical laminate prepared from one or more plies of a resinimpregnated laminate, at least one of such plies being a resinimpregnated laminate of claim
 12. 20. An electrical laminate preparedfrom one or more plies of a resin impregnated laminate, at least one ofsuch plies being a resin impregnated laminate of claim
 13. 21. Anelectrical laminate prepared from one or more plies of a resinimpregnated laminate, at least one of such plies being a resinimpregnated laminate of claim
 14. 22. An electrical laminate preparedfrom one or more plies of a resin impregnated laminate, at least one ofsuch plies being a resin impregnated laminate of claim
 15. 23. Anelectrical laminate prepared from one or more plies of a resinimpregnated laminate, at least one of such plies being a resinimpregnated laminate of claim
 16. 24. An electrical laminate preparedfrom one or more plies of a resin impregnated laminate, at least one ofsuch plies being a resin impregnated laminate of claim 17.